1. Field of the Invention
The present invention relates to a camera lens assembly, and more particularly to an optical image stabilizer mounted to a digital camera or a mobile communication terminal for correcting an image blurred by a hand-shake of a user.
2. Description of the Related Art
A mobile communication terminal equipped with a camera function is being commonly used today.
Just as in a regular camera, images can be blurred using mobile communication terminals.
Although high resolution cameras are available with the progress of the optical technology, optical image stabilizers are needed to reduce the effect of image-blurs from vibrations.
Current technologies for correcting images is classified into two types. One is a DIS (digital image stabilization) or EIS (electronic image stabilization) method, which detects a hand-shake from a photographed image and corrects data stored in a camera device. More specifically, a blurred image is received, then by regulating positions and colors of the image with an electronic method or program, the blurred image can be adjusted.
The electronic image stabilization method has an advantage in that separate mechanical and physical constitutions are required, thus lowering the manufacturing cost. Also, the restriction on the structure is small, and thus can be easily employed. However, since it corrects an image through a software, it requires dedicated memory or a high efficiency camera device and takes longer to correct. Further, since there is a limit in removing an afterimage through a software, the correction rate is undesirably slow.
The other image stabilization technologies is an OIS (optical image stabilization) method, which corrects a shake of a subject image by detecting a hand-shake of a user and then changing the position of an optical lens or a camera device.
Since the OIS method needs a separate drive device, the manufacturing cost therefore increases and a separate installation space is needed. However, since a blur-free image is provided on the camera device, thereby removing an afterimage, the correction rate is over ninety percent. In addition, the OIS method can obtain an image more clearly than that of the EIS method. Therefore, the OIS device is more frequently used in a photography device requiring a high resolution.
Although the technology in which an optical lens is moved to correct an image in a digital camera having a space sufficient for embedding a drive section for driving the optical lens, it is difficult to employ such a technology in a miniaturized digital camera or a mobile communication terminal, which has many spatial restrictions. As a result, research efforts on a technology in which a hand-shake can be corrected by moving a camera lens is actively pursued.
Japanese Patent No. 10-39350 discloses an example of such an optical image stabilizer, which includes an X-axis piezoelectric device and a Y-axis piezoelectric device at the outer periphery of an optical lens, a separate portion for supporting them, whereby the optical lens makes contact to a drive shaft of the piezoelectric device to move the optical lens by a predetermined distance using a frictional force. However, since the outer diameter of the optical lens system increases to install the drive device such as the piezoelectric device at the outer periphery of the optical lens, it is difficult to mount the stabilizer to a mobile communication terminal having a restricted assembly length and diameter. Further, since a considerable drive force must be generated to drive the optical lens of a predetermined weight, there is a limit in miniaturizing the drive device. Lastly, since much electric power is needed, there is a limit in mounting the stabilizer to a portable photography device which uses charging batteries.
Hence, difficulties in designing a miniaturized drive device and the rise of manufacturing costs according to the increase in the number of parts are obstacles in securing the cost competitiveness of a photography device in which an image stabilizer is embedded. Moreover, in the case of a contact-type drive device which uses frictional forces with a drive shaft such as a piezoelectric device, it is difficult to manage the tolerance of the contact surfaces. In the event that the contact surface is worn, malfunction can be generated, thereby lowering the reliability. Furthermore, since a drive circuit for generating and applying a predetermined voltage wave is required to drive the drive device such as the piezoelectric device, the manufacturing cost increases, and there is a restriction in simplifying the photography device.